The discharge lamp used for vehicle headlights is known from JP-A 2007-87683 (KOKAI) (Patent Reference 1) and WO 2007/086527 A1 (Patent Reference 2), and it has a discharge medium which is comprised of a metal halide of sodium, scandium, zinc or the like and a rare gas such as xenon, sealed into a discharge space of an airtight tube with both ends of which are sealed and generates a predetermined light by applying a voltage to electrodes connected to metal foils which are attached to sealing portions by sealing to excite the discharge medium.
But, this type of discharge lamp has a problem that the metal halide sealed in the discharge space reaches to the metal foil through a small gap between the electrode axis and the glass to exfoliate the glass and the metal foil configuring a seal portion, resulting in easily causing crack leak (hereinafter called as foil leak). This problem becomes more conspicuous when a coil is wound around the electrode axis.
According to Patent Reference 1, a hole is formed in the metal foil, and the glass which configures the seal portion is entered into the hole to improve the adhesiveness between the metal foil and the seal portion, thereby suppressing occurrence of foil leak. According to Patent Reference 2, the metal foil surface is fabricated to have an irregular shape by laser to improve the adhesiveness with the seal portion, thereby suppressing the occurrence of foil leak.    Patent Reference 1: JP-A 2007-87683 (KOKAI)    Patent Reference 2: WO 2007/086527 A1